The present invention relates to roof control in underground mines such as coal mines, trona mines, and the like.
A detailed background and description of certain prior art is found in the co-pending, allowed patent application entitled Yieldable Mine Post, Ser. No. 07/503,654 filed Apr. 5, 1990; the entire specification and descriptions therein are fully incorporated herein by way of reference. For a rather extensive treatment as to the background of the art, the reader is respectfully referred to this incorporated patent.
Additional prior art made of record incited in the prosecution of the earlier case by the following patents:
______________________________________ U.S. PAT. NO. 1006163 1538785 3877319 4995567 4006647 4100749 4344719 4302721 FOREIGN PATENTS 2904741 (Germany) 2045312 (Great Britain) ______________________________________
Both in this and in the inventor's prior patent, a telescoping tubular construction is provided. In the latter the innermost post length, mainly in tubular developed form, or simply a slotted tube, is provided, but with the inner tubular post being compressed and tack welded at its slot so that the innermost post length may be conveniently slid into and carried by the outermost post length. For mutual, wall-friction developing purposes, the inner tubular post length is inserted into the outer tubular post length, then the tack welds broken so that the innermost tubular post length expands radially outwardly so as to produce or commence a wall-friction characteristic desired. Subsequent insertion of a wedge in the slotted portion of the innermost tubular post length serves to increase the girth of the innermost tubular post length so as to result in the friction bubble needed, as fully explained in this above-referenced patent. The wall thicknesses of the innermost and outermost tubular post lengths of such prior patent are shown substantially enlarged for convenience of illustration.
The inventor has taken this concept a considerable step further in the present invention in providing innermost and outermost tubular post lengths which, in their nominal dimension, and when telescoped together, provide a space between the outer wall surface of the innermost post length and the inner wall surface of the outermost post length. The innermost post length is configured to produce the pressure bubble needed to offer resistance to end loading of the post construction.